People who could become pregnant shouldn’t take dietary supplements that contain vinpocetine, the Food and Drug Administration warned this week, because the synthetic ingredient could hurt a developing fetus.

The warning comes after a report from the National Toxicology Program (NTP) found that vinpocetine was associated with fetal abnormalities and miscarriage in rats and rabbits. The compound is found in hundreds of supplement products, many of which are marketed—without much evidence—as ways to improve cognition.

Vinpocetine is classified and regulated as a supplement by the Food and Drug Administration (FDA) and is similar to a compound found in periwinkle—however, it’s created synthetically, and has more in common with a pharmaceutical than with products that are typically considered supplements, says Pieter Cohen, a physician at Cambridge Health Alliance and an associate professor at Harvard Medical School. In other countries, it’s a prescription drug, and used to promote blood flow in the brain.

Laws that regulate supplements are supposed to govern products that are derived from or subcategories of foods, like vitamins and minerals. “It’s not supposed to be a backdoor to introduce pharmacological drugs to consumers without FDA approval,” Cohen says. But, he says, that’s essentially what happened with vinpocetine: A supplement maker submitted the compound as a new dietary ingredient in the late 1990s, and even though it probably should have been turned away as an unapproved drug, the agency allowed it through.

“That opened a legal door to market in supplements,” Cohen says. That poses a risk to consumers, because unlike pharmaceuticals, supplements aren’t formally studied for safety and efficacy—they’re under much less stringent oversight. For example, a pharmaceutical drug must undergo multiple phases of clinical trials, which include giving the drug to large and diverse groups of people as well as targeted groups with a specific disorder the drug is meant to treat. In addition, since vinpocetine can be sold over the counter, researchers and pharmaceutical companies are unlikely to study the substance, even though it might have a useful medical purpose. “Who is going to spend money to do clinical trials when people can buy [it] over the counter?” he says. “It’s a huge disincentive to study the drug. No company would spend the money to do the studies.”

In 2016, the FDA announced that it was re-considering vinpocetine’s classification as a supplement. Cohen speculates that’s why the FDA highlighted this particular NTP report: The results could have more of an impact. Vinpocetine isn’t necessarily widely used by people who could become pregnant, specifically—cognitive enhancers are, broadly speaking, primarily used by the elderly and people in the tech industry interested in improving focus, he says. “I suspect the FDA decided, let’s take a deeper dive into safety, and see if in addition to it being a pharmaceutical, what are the biggest safety concerns.”

The NTP regularly studies dietary supplements—because there isn’t much safety research done on supplements, their work fills the gap, wrote a spokesperson from the National Institute of Environmental Health Sciences, which houses the program, in an email to Popular Science. However, most of their reports, regardless of findings, aren’t accompanied by a warning from the FDA, Cohen says.

“Everyone knows that, say, St. John’s Wort is going to be widely available in supplements, and no rat study will change that,” he says. “Here, we’re talking about a pharmaceutical with a very tenuous hold at being allowed on the market. An animal study is certainly not definitive, but it might make a difference between the FDA moving to eliminate and letting it be on the market.”

In a 2015 study, Cohen and his co-authors analyzed products that say they contain vinpocetine, and found that the products that actually contained the product had a wide range of doses. That’s one reason he says no one should take supplements that say they contain it, not just women of childbearing age. “When you’re taking a drug at [an] unpredictable dose, no way you can know what it will do,” he says.

The FDA cites their renewed commitment to addressing the growing dietary supplement market in their warning about vinpocetine. “The FDA will continue to preserve access to safe, well-manufactured, and accurately labeled dietary supplements, while we protect the American public from potentially unsafe or otherwise unlawful products,” they said in the statement.

For Cohen, though, it’s still mostly talk: the agency doesn’t have a good track record of acting on supplement oversight, and often, their actions (which mostly take the form of warnings to companies) don’t result in change. “Hopefully, this could be a signal of a new environment,” he says. “But all of this could be window dressing. We will have to see. They have to follow through.”